The invention relates to a liquid heating bag and a bag heating means, in particular, for heating cooled blood to a temperature suitable for a transfusion. Such a liquid heating bag comprises a flow volume formed from at least two flexible plastic foils which are preferably connected to each other at four delimiting edges, wherein the flow volume has a flat, substantially trapezoidal basic shape which is delimited by the delimiting edges. An inlet line opening and an outlet line opening are provided on the flow volume for a liquid to be heated.
A blood heating system which consists of a blood heating bag and a bag heating means is used for heating natural blood for transfusion purposes or for dialysis as well as for transfusion of blood plasma or other liquids.
Blood is usually kept at a temperature of approximately 4° C. Prior to use, the blood must be heated to body temperature of approximately 37° C. The blood which is used for transfusions must not have an excessively low or an excessively high temperature. In particular, in case of an emergency, the blood must be heated very quickly, since it is not possible to keep heated blood ready for possible emergencies. In case of an emergency, the blood must be heated quickly and also the handling of the blood heating system must be simple and rapid. The stated temperature conditions must be maintained irrespective of the flow rate of the blood through the blood heating system. This flow rate may be over 5 liters per hour for infusions under pressure. To avoid overheating, the temperature of the bag heating means may only be slightly above the body temperature with the consequence that the bag heating means must provide a large heat exchanging surface to obtain sufficient thermal transfer.
Prior art discloses bag heating means of various designs. A distinction can be drawn between bag heating means for inserting a liquid heating bag, having a chamber that can be opened and that is closed during heating of the inserted liquid heating bag, and into which the liquid heating bag is inserted, and bag heating means for inserting a liquid heating bag into a gap formed between two heat exchanger plates that are fixed parallel to each other using fastening means. The bag heating means having a chamber which can be opened are relatively difficult to handle and are therefore of limited use in emergencies.
When a liquid, for example, blood, is heated by means of a blood heating system, gases dissolved in the blood can be released, resulting in the formation of gas bubbles in the liquid heating bag. These gas bubbles must not enter the body of the patient receiving the blood, since they could produce an embolism. Precautions must therefore be taken to avoid the entry of gas bubbles. This can be done, for example, by visual monitoring of the blood transfusion. U.S. Pat. No. 6,572,641 discloses a liquid heating bag of the inventive kind that, in addition to the inlet line opening and the outlet line opening, has a degassing opening terminating in a gas reception volume that is part of the flow volume. This degassing opening is disposed in the region of an upper limiting edge that is to be disposed at the top during liquid heating and is located above the outlet line opening. In this way, upwardly rising gas bubbles are captured in the gas reception volume and are removed through the degassing opening. In this liquid heating bag, the degassing opening extends relatively far into the gas reception volume, so that the liquid level of the liquid to be heated is above the degassing opening. This can result in loss of liquid. For this reason, one free end of a tube connected to the degassing opening has liquid flow prevention means providing a seal against the passage of liquid. In this liquid heating bag, the inlet line opening, the outlet line opening, and the degassing opening are each disposed at different delimiting edges, i.e. sides of the liquid heating bag. This makes handling the liquid heating bag more difficult because tubes connected to the openings lead out of the bag heating means used for heating.
A blood heating system with a more easily handled liquid heating bag of the inventive kind is described in DE 10 2004 026 446 A1. In this liquid heating bag, the inlet line opening and the outlet line opening are disposed on an upper delimiting edge to be disposed at the top during liquid heating. The upper delimiting edge extends sufficiently obliquely with respect to its adjacent delimiting edges that an acute angle is subtended between the upper delimiting edge and a delimiting edge adjacent thereto. This acute angle includes an upper flow volume region into which the outlet line opening opens. Furthermore, a liquid flow guiding seam is provided that is formed by connecting the plastic foils in the region of the flow volume and that divides the upper delimiting edge into a lower inlet line opening region and an upper outlet line opening region. At the openings of this liquid heating bag, the inlet and outlet lines protrude in an ordered fashion upward out of the bag heating means used. However, this liquid heating bag has no degassing opening.
The object of the invention is to provide a liquid heating bag and a bag heating means that avoid the disadvantages of prior art. In particular, the bag should reliably avoid gas bubbles entering the outlet line opening while avoiding loss of the liquid to be heated.